1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method for repairing an LCD device and an LCD device with using the same method, in which an edge of an LCD panel having a gravity defect is cut to exhaust liquid crystals and repaired by a new LCD panel having no gravity defect.
2. Discussion of the Related Art
The demand for various display devices has increased with the development of the information society. Accordingly, much effort has been made to research and develop various flat display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices. Some species of flat display devices have already been applied to displays for various equipment.
Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used due to their thin profile, light weight, and low power consumption. In fact, LCD devices are providing a substitute for cathode ray tube (CRT) devices. In addition to mobile type LCD devices such as displays for notebook computers, LCD devices have been developed for computer monitors and televisions.
To use LCD devices in various fields as a general display, LCD devices must be developed that can implement high quality picture with high resolution and high luminance on a large-sized screen while still maintaining light weight, thin profile, and low power consumption.
A general LCD device includes first and second substrates bonded to each other with a space therebetween, and a liquid crystal layer formed in the space between the first and second substrates by injection. In more detail, the first substrate includes a plurality of gate lines arranged along a first direction at fixed intervals and a plurality of data lines arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel regions are defined by the gate lines and the data lines. A plurality of electrodes are arranged within the pixel regions. A plurality of thin film transistors, formed at regions where the gate lines cross the data lines, apply data signals of the data lines to the pixel electrodes in accordance with signals supplied to the gate lines. Also, the second substrate includes a black matrix layer that prevents light from reaching portions except the pixel regions, R/G/B color filter layers formed to correspond to the pixel regions, for displaying various colors, and a common electrode for producing the image on the color filter layers.
In the aforementioned LCD device, the liquid crystal layer is formed between the first and second substrates. As such, liquid crystal molecules of the liquid crystal layer are driven by an electric field generated between the pixel electrode and the common electrode. Light irradiated through the liquid crystal layer may be controlled by the alignment direction of the liquid crystal molecules, thereby displaying the image.
This kind of LCD device is referred to as a twisted nematic (TN) mode LCD device, which has disadvantageous characteristics such as a narrow viewing angle. To overcome the problem of a narrow viewing angle, an in-plane switching (IPS) mode LCD device has been developed. In the IPS mode LCD device, a pixel electrode and a common electrode are formed in a pixel region of a first substrate in parallel with each other at a fixed interval so that an IPS mode electric field (horizontal electric field) occurs between the pixel electrode and the common electrode, thereby aligning the liquid crystal layer according to the IPS mode electric field. Spacers are formed between the first and second substrates of the aforementioned LCD device to maintain a constant interval for the liquid crystal layer. The spacers may be ball spacers or column spacers. Ball spacers have a spherical shape and are dispersed on the first or second substrates. Also, ball spacers are relatively free in their movement even after the first and second substrates are bonded together. The ball spacers have a small contact area with the first and second substrates. In contrast, the column spacers are formed on the first substrate or the second substrate by an array process. The column spacers are formed on a predetermined substrate in a column shape having a predetermined height. Therefore, the column spacers have a relatively large contact area with the first and second substrates.
Hereinafter, a related art LCD device provided with a column spacer will be described with reference to the accompanying drawings. FIG. 1 is a sectional view illustrating a related art LCD device provided with a column spacer.
As shown in FIG. 1, the related art LCD device provided with a column spacer includes first and second substrates 30 and 40 opposed to each other, a column spacer 20 formed between the first and second substrates 30 and 40, and a liquid crystal layer (not shown) filled between the first and second substrates 30 and 40. The first substrate 30 includes a gate line 31 crossing a data line (not shown) to define a pixel region, a thin film transistor TFT formed on a crossing region of the gate line 31 and the data line, and a pixel electrode (not shown) formed in each pixel region. The first substrate 30 further includes a gate insulating layer 36 formed on the entire surface including the gate line 31, and a passivation layer 37 formed over the gate insulating layer 36. The second substrate 40 includes a black matrix layer 41 corresponding to a region other than the pixel region, a stripe shaped color filter layer 42 corresponding to vertical pixel regions parallel with the data line, and a common electrode or an overcoat layer 43 formed on the color filter layer 42. The column spacer 20 is formed to correspond to a predetermined position above the gate line 31.
In the LCD device provided with the column spacers 20, when an LCD panel 10 is arranged in a vertical direction under a high temperature environment, liquid crystals inside the LCD panel 10 in a height direction expand more than the column spacers 20. In this case, the column spacers 20 may be spaced apart from its opposing substrate 30. At this time, the liquid crystals flow into the space between the column spacers 20 and its opposing substrate 30 and then concentrated on a lower corner, thereby causing light leakage at the lower corner. This is referred to as a gravity defect.
Hereinafter, the principle of the gravity defect will be described with the accompanying drawings. FIGS. 2A and 2B are sectional views illustrating the LCD panel arranged in a vertical direction at a room temperature and a high temperature, respectively, and FIG. 2C is a sectional view illustrating the gravity defect generated from the LCD panel of FIG. 2B.
In case of the LCD panel arranged in a vertical direction as shown in FIG. 2A (a liquid crystal layer 25 is filled between first and second substrates 30 and 40 opposing each other), the liquid crystals are neither expanded nor contracted at a room temperature so that respective regions of the LCD panel are maintained at a uniform thickness.
If the LCD panel of FIG. 2A is subjected to a high temperature environment as shown in FIG. 2B, the liquid crystals 25 between the first and second substrates 30 and 40 expand. At this time, under the high temperature environment, the liquid crystals 25 expand more than the column spacers 20 of a solid state. Therefore, the liquid crystals 25 expand more than a cell gap between the first and second substrates 30 and 40 supported by the column spacers 20.
In this case, if the liquid crystals 25 expand as shown in FIG. 2C, the column spacers 20 are separated from its opposing substrate, i.e., the first substrate 30. At this time, the liquid crystals are gathered on the lower corner adjacent to the ground along the gap between the column spacer and the first substrate due to the effects of gravity. For this reason, the cell gap increases at the lower corner, and light leakage at the lower corner is observed due to excessive liquid crystals. This is known as a gravity defect.
FIG. 3 is a photograph illustrating the gravity defect. As shown in FIG. 3, light leakage is observed at some of the lower corners of the LCD panels where the gravity defects occur. Any LCD panels having such gravity defects must be found and thrown away before distribution of the LCD devices or during their lighting test. Accordingly, it is necessary to prevent the gravity defects to improve productivity of the LCD device.
In summary, the aforementioned related art LCD device has several problems. For example, in LCD devices provided with column spacers, when the LCD panel is arranged in a vertical direction under the high temperature environment, the liquid crystals inside the LCD panel expand more than the column spacers expand in a height direction. Thus, the column spacers may separate from the opposing substrate. At this time, the liquid crystals flow into the space between the column spacers and the opposing substrate. The liquid crystals then concentrate at the lower corner, thereby causing light leakage at the lower corner, known as the gravity defect. The LCD panels having such gravity defects must be found before distribution of the LCD devices, such as during their lighting test, and thrown away. Accordingly, it is necessary to prevent the gravity defect to improve manufacturing of the LCD device.